Display devices that use display panels that do not emit light on their own, such as liquid crystal display panels, are normally combined with an illumination device that illuminates the display panel from behind. A variety of components are used for the light source of this type of illumination device, such as cold cathode fluorescent tubes or light-emitting elements. Light-emitting diodes (hereinafter, referred to as “LEDs”), organic electroluminescent elements, inorganic electroluminescent elements and the like are used as these light-emitting elements, with LEDs now being mainstream. The light source of the illumination device disclosed in Patent Document 1 is also a white LED with a high degree of brightness.
A configuration example of an LED used as a light source is shown in FIG. 7. A package 100 of the LED in FIG. 7 has a light reflecting face 102 for increasing the degree of brightness formed on a substrate 101, and an LED device 103 fixed above the light reflecting face 102 by a die attach adhesive 104. Wire bonding is performed with a metal wire 105 from the light reflecting face 102 to the LED device 103 to complete the electrical connection. The light reflecting face 102 is then enclosed by a reflector 106 made of a synthetic resin with high light reflectance, and a sealing resin 107 is filled inside the reflector 106 to complete the package 100.
The light reflecting face 102 is made of a material that has silver as a main component (as a matter of course, this also includes pure silver). Silver has a very high reflectance of visible light of 90% or above; therefore, it is well-suited to increase the degree of brightness. Silver plating or silver deposition is performed on the substrate 101 to form the light reflecting face 102.
While silver has a high reflectance of visible light, it is susceptible to binding with halogen gas and hydrogen sulfide. If silver makes contact with halogen gas containing a halogen element such as fluorine, chlorine, bromine, or iodine, then a silver halide will form and the silver will darken. Silver sulfide will also form if the silver makes contact with hydrogen sulfide, and the silver will darken. A problem based on this will be explained using FIG. 8.
FIG. 8 shows a group of silver particles (represented by oval shapes) in three vertical tiers. The top tier shows the silver particles formed by silver plating in an orderly arrangement. When halogen is added to this tier, a few of the silver particles bind to the halogen and form a silver halide such as silver chloride, silver bromide, silver iodide, or silver fluoride. The shaded oval shapes in the silver particle group in the middle tier represent silver halides.
When light is radiated on the silver particle group in FIG. 8, the silver halides break down into silver and halogen. This process roughens the surface of the light reflecting face. The silver particle group in the bottom tier represent this condition. If darkening occurs or the surface becomes rough in this way, or in other words, if the light reflecting face is degraded, then the reflectance of the light reflecting face will substantially decrease. As a result, the brightness of the LED package 100 will decrease.
There are components among the constituent members of the illumination device, in which the LED package 100 is included, that generate halogen gas when heated. The use of materials that generate halogen gas is being reduced in order to lessen the release of halogen gas into the natural environment; however, the replacement of halogen that is used as a fire retardant is difficult, and it is not practical to completely remove halogen.
Halogen gas passes through the sealing resin 107 of the LED package 100 to reach the light reflecting face 102. There are also cases in which tearing occurs at the boundary of the sealing resin 107 and the reflector 106, or at the boundary of the sealing resin 107 and the substrate 101, and halogen gas enters through the resulting gap. Hydrogen sulfide, which is contained in the atmosphere at hot springs and the like, causes problems similar to halogen gas.
To address the above-mentioned problems, a backlight device in Patent Document 1 includes an LED package with an LED chip and a light reflecting face that contains silver as a main material, and an optical member that adjusts light emitted from this LED package. The structure of the optical member in the backlight device is such that the release of halogens is small enough that silver halides do not form on the light reflecting face.
A reduction in reflectance of the light reflecting face can also be prevented by methods such as adopting a configuration with low oxygen transmittance for the sealing resin, or applying a coating on the light reflecting face.